System and method for reducing radiator sizes for low temperature fuel cell systems

ABSTRACT

A fuel cell cooling system includes a fuel cell having a liquid loop that produces water vapor. An antifreeze cooling loop includes an inductor that receives the water vapor and introduces the water vapor to an antifreeze. The water is separated from the antifreeze and returned to the liquid cooling loop as liquid water after the mixture of condensed water vapor and antifreeze has passed through a radiator. Water in the liquid cooling loop exits the fuel cell and passes through a restricting valve thereby lowering the pressure of the water. A flash cooler downstream from the restricting valve collects the water vapor and provides it to the inductor in the antifreeze cooling loop. The flash cooling in the first cooling loop provides a first cooling capacity that is low temperature and pressure compatible with fuel cell operation.

This application is a divisional application of U.S. application Ser.No. 12/096,828, now U.S. Pat. No. 8,192,883, filed on Jun. 10, 2008,which was the National Stage of International Application No.PCT/US06/00859, filed on Jan. 10, 2006.

BACKGROUND OF THE INVENTION

This invention relates to a fuel cell cooling system using an antifreezeloop to supplement the cooling capacity of the liquid cooling loop.

Fuel cells are increasingly used for transportation applications. Fuelcells having proton exchange membranes (PEM) for these applicationsrequire large radiators to achieve a desired water balance within thefuel cell at high altitudes and/or high ambient temperatures. The fuelcell includes a stack having a cathode, anode and PEM electrolyte. Thestack coolant inlet temperatures typically must be less than 60° C. toachieve the desired water balance. As a result, in one example, aradiator must be capable of rejecting between 70-80 kW of heat whileproviding a coolant return temperature to the fuel cell of less than 60°C.

The cell stack typically includes a liquid cooling loop, and anintermediate heat exchanger is used to separate the liquid coolant loopfrom an antifreeze that circulates through the radiator. The antifreezeis needed to prevent the radiator from freezing so that the fuel cellcan operate in cold weather applications.

It is also desirable to operate the fuel cell near ambient pressure.Therefore, what is needed is a cooling system operating at near ambientpressure and at a temperature of 60° C. or lower in the fuel cell whilerejecting heat from the antifreeze/water loop at higher temperatures tominimize radiator size.

SUMMARY OF THE INVENTION

The present invention provides a fuel cell cooling system including afuel cell having a liquid water loop that produces low pressure watervapor. An antifreeze cooling loop includes an inductor that receives thewater vapor, pressurizes the water vapor and introduces the water vaporto an antifreeze. The water is separated from the antifreeze andreturned to the fuel cell cooling loop as liquid water after the mixtureof condensed water vapor and antifreeze has passed through a radiator.Preferably, the antifreeze is an immiscible antifreeze so that the watercan be easily separated from the antifreeze.

Water in the liquid cooling loop exits the fuel cell and passes througha restricting valve thereby lowering the pressure of the water. A flashcooler downstream from the restricting valve collects the water vaporand provides it to the inductor in the antifreeze cooling loop. Theflash cooling in the first cooling loop removes fuel cell waste heat asvaporized water which passes on to the antifreeze cooling loop. Theantifreeze cooling loop is higher pressure and condenses the water vaporat higher temperatures. Higher radiator temperatures minimize radiatorsize.

Accordingly, the present invention provides a high temperature coolingsystem combined with near ambient pressure and low temperature coolingin the fuel cell without increasing the size of the radiator in theantifreeze cooling loop.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a schematic of one example fuel cell cooling system accordingto the present invention.

FIG. 2 is a schematic of an inductor shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A schematic of a fuel cell system 10 is shown in FIG. 1. It should beunderstood, however, that the fuel cell system 10 is only exemplary.That is, additional, fewer and/or different components may be usedand/or the components rearranged and still fall within the scope of thisinvention.

The fuel cell system 10 includes a fuel cell 12 having an anode 14receiving fuel 16 such as hydrogen. The fuel cell 12 also includes acathode 17 receiving an oxidant 18 such as air. A PEM 20 is arrangedbetween the anode 14 and cathode 17.

A cooler 22 receives liquid water that is produced within the fuel cell12. The liquid water within the cooler 22 is circulated throughout afirst cooling loop 24 by a pump 26. The fuel cell 12 includes an inlet28 and an outlet 30. It is desirable for the liquid water entering theinlet 28 to be at approximately 60° C. It should be understood, however,that the pressures and temperatures associated with the variouscomponents in FIG. 1 are exemplary only.

The liquid water exiting the fuel cell 12 flows through a restrictorsuch as a restricting valve 32 to lower the pressure of the liquidwater. An orifice may also be used as a restrictor, for example. Theliquid water exiting the restricting valve 32 enters a flash cooler 34that collects water vapor since the boiling point of the water has beensignificantly lowered by the reduced pressure. A water vapor line 36fluidly connects the flash cooler 34 to a second cooling loop 38.Vaporization of the liquid water by the restriction water 32 and flashcooler 34 provides a first cooling capacity.

The second cooling loop 38 includes a fluid connector such as aninductor 40 that receives the water vapor. The inductor 40 increases thepressure of the water vapor so that the water vapor condenses. Anexample inductor 40 is shown in FIG. 2. A compressor may also be used asan inductor. The second cooling loop 38 includes an antifreeze,preferably an antifreeze that is immiscible.

Referring to FIG. 2, the inductor 40 includes a nozzle 54 having an exit58. The water vapor is provided by an orifice 60 of the water vapor line36 near the exit 58. A diffuser 56 may be arranged near the exit 58downstream from the nozzle 54. A throat 62 may be provided between thenozzle 54 and diffuser 56 with the orifice 60 arranged at the throat. Itshould be understood that the structure described and shown in FIG. 2 isonly exemplary.

The inductor 40 produces a mixture of the immiscible antifreeze andcondensed water vapor. The mixture is circulated by a pump 42. Aradiator 44 receives the mixture, and a fan 46 blows air through theradiator 44 to cool the mixture. A separator 48 receives the mixture andseparates the immiscible antifreeze and liquid water. Any inert gasesare released by an exit 52 in the separator 48. A liquid water returnline 50 fluidly connects the separator 48 and first cooling loop 24 sothat the liquid water that was originally introduced to the secondcooling loop as water vapor is returned to the first cooling loop 24.

In prior art systems, the radiator needed to provide the entire desiredcooling capacity for the fuel cell 12 at relatively low fuel celloperating temperatures. This requires a relatively large radiator. Inthe inventive fuel cell system 10, the vaporization of the water in thefirst cooling loop 24 reduces the cooling capacity needed from theradiator 44. The pressurization of cooling water vapor from the fuelcell cooling loop permits the use of a higher radiator temperature inthe antifreeze cooling loop. This results in a smaller radiator than theprior art systems.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A method of cooling a fuel cell comprising: a) evaporating a firstcoolant from the fuel cell in a first cooling loop to produce a firstcoolant vapor and provide a first cooling capacity; and b) mixing thefirst coolant vapor with a second coolant in a second cooling loop toproduce a mixture and provide a second cooling capacity, wherein thesecond cooling loop includes an inductor including a nozzle and an exitjoined at a throat, and an orifice arranged near the exit; a water vaporline fluidly connects the first coolant loop and the orifice andconfigured to introduce the first coolant vapor to the throat; and themixing step includes the nozzle receiving the second coolant at thenozzle to provide the mixture of the first coolant vapor and the secondcoolant at the exit.
 2. The method of claim 1, wherein step a) includesreducing a pressure of the first coolant.
 3. The method of claim 1,wherein step b) includes condensing the first coolant vapor into liquidfirst coolant in the second cooling loop.
 4. The method of claim 3,comprising step c) separating the liquid first coolant from the secondcoolant.
 5. The method according to claim 4, comprising step d)returning the liquid first coolant to the first cooling loop.
 6. Themethod according to claim 1, wherein step a) produces a firsttemperature associated with the first cooling capacity, and step b)produces a second temperature associated with the second coolingcapacity, the second temperature higher than the first temperature. 7.The method of claim 1, wherein the second cooling loop is separating thefirst coolant from the second coolant and returning the first coolant tothe first cooling loop as liquid first coolant.
 8. The method of claim7, wherein the second coolant is selected from the group consisting ofan antifreeze, an immiscible fluid and a combination thereof.
 9. Themethod of claim 8, wherein the first coolant is water, and the secondcoolant is an immiscible fluid.
 10. The method of claim 7, wherein thefirst cooling loop includes a restrictor receiving the first coolantfrom the fuel cell and lowering a pressure of the first coolant toproduce the first coolant vapor, and a flash cooler collecting the firstcoolant vapor from the first coolant exiting the restrictor whiledropping the temperature of the first coolant.
 11. The method of claim10, wherein the water vapor line fluidly connects the first coolantvapor to the inductor in the second cooling loop, the inductor raisingthe pressure of the first coolant vapor and condensing the first coolantvapor.
 12. The method of claim 7, wherein the inductor condenses thefirst coolant vapor to the liquid first coolant, a pump circulates thefirst and second coolants to a heat exchanger for cooling, and a returnline fluidly connects the first and second cooling loops and providesthe cooled first coolant to the first cooling loop.
 13. The methodaccording to claim 7, wherein inductor includes a diffuser arranged nearthe exit downstream from the nozzle, and the orifice is arranged at thethroat.